Excessive levels of arsenic have been detected in the air around Wainuiomata in a year- long study.

The air at the test site was 30 per cent over national guideline levels set by the Ministry for the Environment.

The arsenic probably came from residential fireplaces burning wood that had been treated with the chemical as a preservative, researchers said. Residents burning treated wood were exposing themselves to much higher levels.

Arsenic is a known carcinogen, causing lung cancer. The study also showed atmospheric arsenic rose dramatically in winter. Tests showed 7.1 nanograms of arsenic per cubic metre of air, above the national guideline of 5.5 nanograms.